Deflectable catheter with bonded center strut and method of manufacture for same

ABSTRACT

A catheter for diagnosing or treating the vessels found within a body or body space includes a center strut that is bonded, preferably thermally, along its longitudinal axis with the thermoplastic tubular member within which it is housed. The tubular member preferably has three layers: an inner layer, a braided layer and an outer layer. The composite catheter is made using a process in which two half-cylinder shaped mandrels are placed on each side of the center strut while the strut is heated in order to cause the thermal bonding. The bonded center strut provides in-plane deflection and improved transfer of torque to the tip of the catheter.

FIELD OF THE INVENTION

The present invention relates to a medical device for use in the vesselof a patient for the purpose of diagnosing or treating the patient, suchas mapping tissue and/or ablating tissue using radio frequency (RF) orother sources of energy. More particularly, the invention relates to adeflectable catheter having a center strut bonded into the deflectingportion of the catheter tip to define an inseparable composite tipstructure that maximizes the open internal volume of the catheter tipand the torsional rigidity of the catheter tip while minimizing theoutside diameter of the catheter tip and providing uniform on-plane tipdeflection. The invention also covers a method for making the same.

BACKGROUND OF THE INVENTION

Many abnormal medical conditions in humans and other mammals have beenassociated with disease and other aberrations along the lining or wallsthat define several different body spaces. In order to treat suchabnormal conditions of the body spaces, medical device technologiesadapted for delivering various therapies to the body spaces using theleast invasive means possible.

As used herein, the term “body space,” including derivatives thereof, isintended to mean any cavity within the body which is defined at least inpart by a tissue wall. For example, the cardiac chambers, the uterus,the regions of the gastrointestinal tract, and the arterial or venousvessels are all considered illustrative examples of body spaces withinthe intended meaning.

The term “vessel,” including derivatives thereof, is herein intended tomean any body space which is circumscribed along a length by a tubulartissue wall and which terminates at each of two ends in at least oneopening that communicates externally of the body space. For example, thelarge and small intestines, the vas deferens, the trachea, and thefallopian tubes are all illustrative examples of vessels within theintended meaning. Blood vessels are also herein considered vessels,including regions of the vascular tree between their branch points. Moreparticularly, the pulmonary veins are vessels within the intendedmeaning, including the region of the pulmonary veins between thebranched portions of their ostia along a left ventricle wall, althoughthe wall tissue defining the ostia typically presents uniquely taperedlumenal shapes.

One means of treating body spaces in a minimally invasive manner isthrough the use of catheters to reach internal organs and vessels withina body space. Electrode or electrophysiology (EP) catheters have been incommon use in medical practice for many years. They are used tostimulate and map electrical activity in the heart and to ablate sitesof aberrant electrical activity. In use, the electrode catheter isinserted into a major vein or artery, e.g., the femoral artery, and thenguided into the chamber of the heart that is of concern in order toperform an ablation procedure.

Steerable catheters are generally well-known. For example, U.S. Pat. No.RE 34,502 describes a catheter having a control handle comprising ahousing having a piston chamber at its distal end. A piston is mountedin the piston chamber and is afforded lengthwise movement. The proximalend of the catheter body is attached to the piston. A puller wire isattached to the housing and extends through the piston and through thecatheter body. The distal end of the puller wire is anchored in the tipsection of the catheter to the side wall of the catheter shaft. In thisarrangement, lengthwise movement of the piston relative to the housingresults in deflection of the catheter tip section. The design describedin U.S. Pat. No. RE 34,502 is generally limited to a catheter having asingle puller wire.

Bidirectional steerable catheters are also generally well known, as avariety of designs have been proposed. In many such designs, such asthose described in U.S. Pat. Nos. 6,066,125, 6,123,699, 6,171,277,6,183,463 and 6,198,974, a pair of puller wires extend through a lumenin the main portion of the catheter shaft and then into opposing offaxis lumens in a deflectable tip section where the distal end of eachpuller wire is attached to the outer wall of the deflectable tip.Pulling one wire in a proximal direction causes the tip to deflect inthe direction of the off axis lumen in which that wire is disposed.

In other designs, such as those described in U.S. Pat. No. 5,531,686,the puller wires are attached to opposite sides of a rectangular platethat is fixedly mounted at its proximal end and extends distally withina lumen in the tip section. In this arrangement, pulling one of thewires proximally causes the rectangular plate to bend in the directionof the side to which the pulled puller wire is attached, thereby causingthe entire tip section to deflect.

In all of the designs for a steerable catheter, the method ofmanufacturing is generally complex, time-consuming and does notnecessarily result in a catheter that accurately translates thelongitudinal motion of the pull wire into uniform on-plane tipdeflection.

SUMMARY OF THE INVENTION

The invention is directed to an improved steerable catheter, moreparticularly a bidirectional steerable catheter. The catheter comprisesan elongated, tubular catheter body having at least one lumen extendingtherethrough and a deflectable tubular tip section having a center strutand two half-cylindrical lumens extending therethrough. The center strutis bonded, preferably thermally, to the interior of the tubular cathetersubstantially along the entire length of the center strut therebycreating an inseparable tip structure.

The catheter further comprises first and second puller wires havingproximal and distal ends. Each puller wire extends from a control handleat the proximal end of the catheter body through a lumen in the catheterbody and into one of the lumens in the tip section. The puller wires maybe disposed in a tubular sleeve dimensioned so as to maintain the pullerwires in close adjacent relationship. The distal ends of the pullerwires are fixedly attached either to opposite sides of the center strut,to the tip electrode or the tubular structure of the distal tip sectionof the catheter.

The control handle includes a steering assembly having a lever armcarrying a pair of pulleys for drawing corresponding puller wires todeflect the tip section of the catheter. The pulleys are rotatablymounted on opposing portions of the lever arm such that one pulley ismoved distally as the other pulley is moved proximally when the leverarm is rotated. Because each puller wire is trained on a respectivepulley, rotation of the lever arm causes the pulley that is movedproximally to draw its puller wire to deflect the tip section in thedirection of the off-axis lumen in which that puller wire extends.

Specifically, the present invention is a composite catheter tipcomprising an extruded thin walled elastomeric tube spirally wrappedwith a reinforcing braid wherein the elastomeric tube that has a centerstrut comprised of a thin elongated rectangular metallic strip whereboth thin longitudinal sides (edges) of the said strip are bonded,preferably thermally, to the inside wall of the elastomeric tube therebycreating a composite structure with inseparable members. The term“inseparable” is used to denote the creation of a composite structurebetween the elastomeric tube and the metallic strip so that any attemptto separate the elastomeric tube and metallic strip would causeirreversible destruction of the composite structure.

This composite tip structure provides two enclosed, largediametrically-opposed, half moon shaped lumens extending through the tipproviding space for wiring, sensors, fluid carrying tubing and the like.The strut separating the half moon shaped lumens can be constructed fromany of a number of superelastic (metallic) alloys such as nitinol, betatitanium or spring tempered stainless steel. This composite catheter tipdesign maximizes the cross-sectional area of the open lumens in thecatheter tip and torsional rigidity of the catheter tip while minimizingthe outer diameter of the catheter tip by providing a single uniformarea moment of inertia at any cross section of the longitudinal axis ofthe catheter tip because the bonded center strut and elastomeric tubeare not allowed to move with respect to each other during tipdeflection. This composite structure provides uniform on-plane tipdeflection and uniform torque and deflection forces regardless of thetip deflection angle because the tip cross-sectional area moment ofinertia remains constant along the entire tip length during tipdeflection. All known prior art tip designs exhibit varyingcross-sectional area moments of inertia during tip deflection becausethe inner strut and outer elastomeric tube are fixed to each other onlyat their proximal and distal end locations and the strut and outer tubemove with respect to each (other) during tip deflection. In all priorart designs, the combined centroidal axis of the independently movingstrut and outer tube is continuously variable during tip curvature sincethe absolute distance between the centroidal axis of the whole (strutand outer tube) and the centroidal axis of each of the parts isvariable. This produces non-uniform torque and deflection forces thatare dependent on the degree of tip curvature.

The deflection curve profile of the catheter tip can be modified byvarying the area moment of inertia of the strut cross sectionperpendicular to the struts longitudinal axis by utilizing cutting orcoining operations that either remove material or change the materialthickness in various portions of the center strut cross section. Thecomposite deflecting tip with a bonded center strut has a large width tothickness ratio thus providing a first centroidal axis that has a largearea moment of inertia and a second corresponding low area moment ofinertia about a centroidal axis orthogonal to the first centroidal axisthereby providing exceptional on-plane deflection characteristics.

The method of the present invention results in a single unifiedhigh-performance composite structure for the deflecting tip assembly ofa deflectable catheter that combines the properties of elastomers andmetals and eliminates extruded core lumens. The two half-cylindricallumens created by the bonded strut provide a large volume in which toplace wiring, tip force and location sensors and tip irrigation lumens.Alternatively, an intermediate portion between the deflectable tipsection and the tip electrode can be provided in which there is nocenter strut and which provides even greater room for temperature andlocation sensors. Catheter tip diameters can be reduced since theworking volume of the tip lumen is maximized with this design.

In a preferred embodiment of the catheter an elongate tubular memberhaving a proximal end and a distal end and having a lumen is thermallybonded to the longitudinal edges of a center strut that extends in thedeflectable portion of the catheter. This bonding creates an inseparablecomposite structure from the elongate tubular member and the centerstrut.

A tip electrode is disposed at the distal end of the tubular member. Amolded coupling has a distal portion adapted to receive a portion of theproximal end of the tip electrode and a proximal portion having at leastone slot adapted to receive at least one of the first or secondlongitudinal edges of the center strut.

The distal end of the center strut comprises at least one snap-fit notchand the molded coupling further comprises at least one snap-fit wedgeadapted to receive the snap-fit notch. This construction enables therapid assembly of the tip electrode and the composite tubular member andcenter strut.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-C are a planar views of a deflectable EP catheter with rockertype deflection control handle in accordance with the present invention.

FIG. 1D is a planar view of the friction control knob located on therocker type deflection control handle.

FIG. 2 is a longitudinal cross-sectional view of the deflectable distaltip section and a portion of the proximal section of the catheter ofFIG. 1.

FIG. 3 is a cross-sectional view of the tubular section of the EPcatheter of FIG. 2 through line A-A.

FIG. 4 is an exploded perspective view of the distal tip of anembodiment of a deflectable catheter in accordance with the presentinvention.

FIG. 5 is a perspective view of a tip electrode of the deflectable tipsection of a catheter in accordance with the present invention.

FIG. 6 is a cross-sectional perspective view of a molded coupling of thedeflectable tip section of a catheter in accordance with the presentinvention.

FIG. 7 a is a planar view of a puller wire for use in the deflectabletip section of a catheter in accordance with the present invention.

FIG. 7 b is a perspective view of the distal section of a deflectablecatheter in accordance with the present invention.

FIG. 8 is an elevational view of a center strut in accordance with afurther embodiment the deflectable tip section of a catheter inaccordance with the present invention.

FIG. 9 is a perspective view of the device for manufacturing thedeflectable tip section of a catheter in accordance with the presentinvention.

FIG. 10 is a perspective view of the distal tip of a deflectablecatheter in accordance with the present invention.

FIG. 11 is a perspective view of the distal tip of a deflectablecatheter in accordance with the present invention.

FIG. 12 is a perspective view of a device for manufacturing thedeflectable tip section of a catheter in accordance with the presentinvention.

FIGS. 13A-D depict various control signals and a schematic for thecontrol circuitry for use in the manufacture of a deflectable catheterin accordance with the present invention.

FIGS. 14A-D depict various control signals and a schematic for analternative embodiment of the control circuitry for use in themanufacture of a deflectable catheter in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A-C depict a planar view of an embodiment of a deflectablecatheter in accordance with the present invention. As shown in FIG. 1B,a preferred catheter 100 comprises an elongated tubular catheter bodyhaving a proximal section 32, a distal tip section 34 and a controlhandle 36 at the proximal end of the proximal section 32. Tip electrode38 and optional ring electrode 40 are placed at or near deflectabledistal tip section 34 so as to provide a source of ablation energy ifthe desired device is an RF ablation catheter or for receivingelectrical signals if the catheter is a diagnostic EP mapping catheter.Control handle 36 may be one of many designs capable of placing apulling force on puller wires used to deflect the deflectable tipsection 34. Preferably, control handle 36 is the handle used in theBiosense EZ-Steer bidirectional family of products which control handleis depicted in FIGS. 1A-C. The “rocker” type lever 37 pulls one of twopuller wires to deflect the catheter tip in one direction (FIG. 1A) thencan alternatively select the second (opposite) puller wire to deflectthe catheter tip in the other direction (FIG. 1C). The control handle 36also had an adjustable friction control knob 37 a shown in FIG. 1D thatallows the operator to use the rocker lever 37 in a free state or toadjust the tension to lock the rocker level 37 and the deflected tip inplace. The amount of friction in the movement of the rocker lever 37increases as the friction control knob 37 a is rotated clockwise untilit reaches the fully locked position.

FIG. 2 depicts a cross-sectional view of the transition from proximalsection 32 and deflectable section 34 of catheter 100 takenperpendicular to the center strut 80 that forms a portion of thecatheter and FIG. 3 depicts the cross-section of the catheter of FIG. 2through line A-A. Catheter 100 comprises an elongated tubularconstruction having a central lumen 58 through the distal portion 32 andtwo half-cylindrical lumens 58 a and 58 b in the deflectable tip portion34. The proximal section 32 is flexible but substantiallynon-compressible along its length. Proximal section 32 can be made ofany suitable construction and made of any suitable material. Thepreferred construction comprises an outer wall 30 made of Pellethane orPEBAX and an optional inner wall 18. The outer wall 30 may also comprisean imbedded braided mesh of stainless steel or similar material toincrease torsional stiffness so that when control handle 36 is rotatedthe distal send of proximal section 32 as well as the distal section 34will rotate in a corresponding manner.

The overall length of the length of the catheter will vary according toits application for use but a preferred length is between approximately90 and 120 cm and more preferably between approximately 100 and 110 cm.The outer diameter of the proximal section 32 is also a designcharacteristic that varies according to the application of the catheterbut is preferably less than approximately 8 French (Fr). Optional innerwall 18 comprises a polymeric tube which may optionally bespirally-sliced and is sized so that the outer diameter is about thesame size or slightly smaller than the inner diameter of outer wall 30thereby providing additional stiffness which can be controlled by thepitch angle of the spiral slice.

In the embodiment shown, the distal section 34 and the proximal section32 are separate structures that have been fixedly attached to eachother. Proximal section 32 and distal section 34 may be attached using apolyurethane adhesive at the joint 35 between the two sections. Othermeans of attachment include joining the proximal and distal sectionsusing heat to fuse the sections together.

In the EP catheter of the present invention, tip electrode 38 andoptional ring electrodes 40 shown in FIGS. 1A-1C are each electricallyconnected to one of the bundle of lead wires 70. Each wire in the bundleof lead wire 70 extends from the control handle 36 through the lumen 58in the proximal section 32 and through one of lumens 58 a or 58 b indistal section 34 to tip electrode 38 and optional ring electrode (orelectrodes) 40. The proximal end of each lead wire 70 is connected to anappropriate connector (not shown) in the control handle 36 which can beconnected to a suitable source of RF energy or to an EP mapping or otherdiagnostic or therapeutic system.

Irrigation lumen 90 provides a conduit for transporting fluid from theproximal end of the catheter to the distal tip portion 34. Irrigationlumen 90 is in fluid communication with one or more fluid ports in thetip electrode 38. FIGS. 4 and 5 depict on possible arrangement ofirrigation fluid ports 439 in a tip electrode. Irrigation lumen 90 isused to transport an irrigation fluid through the catheter and outthrough the fluid ports in the tip in order to reduce coagulation ofbodily fluids such as blood at or near the tip electrode.

In a bidirectional catheter a pair of puller wires 44 a and 44 b extendthrough the through lumen 58 in the proximal section 32 and each extendthrough one of lumens 58 a and 58 b in distal section 34. The pullerwires are made of any suitable material such as stainless steel orNitinol wire or a non-metallic yarn such as Vectran® material.Preferably, each puller wire 44 is covered with a lubricious coatingsuch as PTFE or a similar material. Each puller wire 44 extends from thecontrol handle 36 to near the tip of distal section 34.

A sleeve or sleeves (not shown) may be used to house the puller wiresproximally to the soft tip of the catheter. The sleeve is used to keepeach puller wire on its respective sides of the center strut. Forbi-directional deflection the opposing puller wires will always beplaced in a separate lumen. With this design placing multiple pullerwires in one lumen would be used for achieving different deflectioncurves in one deflection direction. Such a sleeve may be made of anysuitable material, e.g., polyamide or polyimide.

Examples of other suitable control handles 36 that can be used with thepresent invention are described in U.S. Pat. Nos. 6,123,699, 6,171,277,6,183,463 and 6,198,974 the disclosures of which are hereby incorporatedby reference. In such control handles proximal movement of the thumbcontrol relative to the handle housing results in proximal movement ofthe first piston and first puller wire relative to the handle housingand catheter body, which results in deflection of the tip section in thedirection of the lumen into which the first puller wire extends. Distalmovement of the thumb control relative to the handle housing results indistal movement of the first piston, causing proximal movement of thesecond piston and puller wire relative to the handle housing andcatheter body, which results in deflection of the tip section in thedirection of the lumen into which the second puller wire extends.Additional configurations of puller wires 44 and gearing within thecontrol handle may be used such as those disclosed in U.S. Pat. No.7,077,823 which is also hereby incorporated by reference.

The distal section 34 is comprised of an inner layer 62, braid layer 64and outer layer 66 of the distal tip section described in greater detailbelow with respect to the method of manufacturing the catheter of thepresent invention discussed below with reference to FIG. 12.

Additionally, a safety wire 95 may be used to secure the tip electrodeto the catheter shaft so as to prevent detachment of the tip electrode.The safety wire is preferably a 0.0065 inch diameter monel which isrouted through the lumen 58 in the proximal portion 32 of the catheteras well as through one of the two lumens 58 a or 58 b in the distal tipportion 34. The distal end of the safety wire is attached to the tipelectrode 38 while the proximal portion is attached to an anchor pointinside the control handle 36.

FIG. 4 depicts an exploded view of the distal tip of a deflectablecatheter in accordance with the present invention. FIG. 5 is aperspective view of tip electrode 438. Tip electrode 438 depicted inFIGS. 4 and 5 is a machined metallic electrode comprised of a metal thatis non-reactive in bodily fluid such as of gold, platinum, palladium oran alloy thereof. Tip electrode 438 may also be made of a first metalsuch as copper, silver, gold, aluminum, beryllium, bronze, palladium oralloys thereof which is then plated either internally and/or externallywith a non-reactive metal such as gold, platinum, palladium or an alloythereof. Tip electrode 438 may include a plurality of irrigation ports439 connected to a central irrigation lumen 440 although such ports andlumens are optional. The proximal end of tip electrode 438 comprises abase 437 having a smaller diameter than the remainder of the tipelectrode and adapted to fit coupling 442. Base 437 may include aplurality of serrations 437 a that improve the bonding of tip electrode438 into coupling 442. Base 437 of the tip electrode 438 is heat bondedor ultrasonically welded to the coupling 442. Tip dome 438 a may bemachined to provide a rounded atraumatic distal tip in order to reducetissue damage during placement and/or use of the catheter. Lumen 495provides a passageway for safety wire 95 and lumen 470 provides apassageway for lead wire 70 that provide energy to the tip electrode438. Lead wire 70 is attached to tip electrode 438 using an electricallyconductive solder or epoxy.

Injection molded coupling 442 depicted in FIGS. 4 and 6 has a distalsection 443 with an internal diameter at its distal end adapted toreceive the base 437 of tip electrode 438 and has a proximal section 441with a slot 441 a adapted to receive the distal end 480 of the centerstrut 80. Coupling 442 is injection molded from a medical grade polymersuch as PEEK, ABS or Polycarbonate or other appropriate material knownto one skilled in the art. Distal end 480 of center strut 80 alsoincludes a snap-fit notch 481 adapted to lock over snap-fit wedge 441 bin the coupling 442 thereby providing a mechanism for the quick assemblyof the distal section of the deflectable catheter which method isdescribed in greater detail below. Puller wire anchor holes 444 a and444 b are lumens that are adapted to receive puller wires 44 a and 44 b.Puller wires adapted for this use are shown in FIG. 7A. Puller wires 44a and 44 b for use in this embodiment are preferably made of Vectran®wire which has had a ball of epoxy 444 c attached to its distal end. TheVectran® wire should be cleaned with alcohol and/or an ultrasonic bathbefore application of a ball of epoxy that is then cured underultraviolet light. It is important that the epoxy be well fixed to thedistal end of the puller wires 44 a and 44 b. Alternatively, the pullerwire could be high strength stainless steel (304V) to which a ball isproduced at one end using a high-speed laser melting process.

A single puller wire 44, made of a non-metallic yarn such as Vectran®material, may be attached to the distal end of the catheter by threadingthe puller wire through one or more anchor holes 82 a-e in center strut80 so that the opposing ends of the puller wire, 44 a and 44 b, resideon opposing sides of the center strut as depicted in FIG. 8. Such anchorholes 82 a-e in center strut 80 preferably have a diameter of 0.015 inchand are spaced apart by approximately 0.078 inch. Such anchor holes maybe placed in the center strut 80 by laser cutting, punching anddrilling. The number of holes on the strut, and the placement of thepuller wires in one or more anchor holes 82 a-e will alter the curveshape and allow for both symmetric and asymmetric curve designs. Forcreating a symmetric curve the opposing ends of the puller wires wouldexit the same anchor hole towards opposing sides of the strut. Means forchanging curve shape can be controlled by the distance between anchorholes used for the opposing ends of the puller wire. When the end ofeach of the pull wires 44 a and 44 b are attached to opposing sides ofthe center strut 80, pulling pull wire 44 a or 44 b in the proximaldirection will cause the distal end of the catheter 100 to deflectin-plane in the direction of the off-axis lumen in which the respectivepuller wire extends.

An alternate embodiment (not shown) uses two puller wires with metallicferrules or plastic slugs to constrain the puller wires in theirrespective anchor hole located in the center strut. The puller wirewould be threaded through the center strut on one side using the ferruleas a constraint from pulling completely through the anchor hole. Anadditional method for anchoring the puller wires is soldering, weldingor using an adhesive to attach them to the center strut.

Alternatively, the puller wires do not need to be attached to the centerstrut. A puller wire or puller wires could be attached to the tip domeor the distal end of the catheter's soft deflectable tip section. FIGS.9-11 show multiple configurations of tip electrodes 38 that are adaptedto receive a single puller wire 44. The single puller wire 44 connectedto the tip electrode 38 provides bi-directional control. To achievethis, a single puller wire is threaded through the dome electrode withthe opposite sides of the puller wire residing on opposite sides of thecenter strut. Deflection direction will correspond with the path ofleast resistance. Moreover, individually manipulating a puller wire willresult in in-plane deflection in the direction of the off-axis lumen inwhich the respective puller wire extends. Such embodiment directlysupports symmetric curve designs.

FIGS. 10 and 11 depict hollow tip electrodes 38 that are adapted toreceive a plug 45 which is force fit into the hollow dome. Puller wire44 is threaded through the plug. One or more puller wires may beanchored in this manner. The puller wire is constrained in place oncethe plug is appropriately placed in the tip electrode.

FIG. 7B depicts another embodiment of the distal tip section of thecatheter 100 where the puller wires are attached to the side wall of thedistal tip section 34 of catheter 100. A small hole 71 is drilledthrough the inner layer 62, braid layer 64 and outer layer 66 of thedistal tip section. After the hole 71 is drilled, a grinder is used tolightly reduce the outer profile around the hole by removingapproximately length=0.04″ depth=0.013″ of material. A stainless steelpuller wire bar 72 is attached to the distal end of the puller wire 44via crimping to a ferrule or other means of adhesion. When the pullerwire 44 is brought through the anchor window the bar rests on the outerprofile of the thermoplastic soft deflectable tip section. Polyurethaneis used to pot over the puller wire bar 72 thereby rebuilding theoriginal profile of the distal tip section 34. In this manner eachpuller wire may be anchored to the outer periphery of the catheter 100at any location along the longitudinal axis of the distal tip section34. It is possible to anchor multiple puller wires in this manner, eachon opposing sides of the center strut. Changing the location of theanchoring location changes the deflection profile of the catheter.

The proximal end of the center strut 80 extends out of the proximal endof the soft deflectable tip portion. The proximal end of the centerstrut may be tapered so it can be readily placed within the proximalsection 32 of the catheter helping to support the transition area. Asleeve preferably composed of PTFE may be placed over the taperedportion of the center strut constraining the puller wires and therebypreventing them from crossing. The sleeve is form fitting so it is tightaround the center strut and wires but not so tight as to prevent thepuller wires from readily moving in the longitudinal direction.

FIG. 12 depicts a device for manufacturing the distal tip section of thepresent invention. The inner layer 62 of the distal section 34 of acatheter in accordance with the present invention is produced byextruding a thin layer of a thermoplastic elastomeric material,preferably between 0.0025-0.0035 inch in thickness, over an acetylpolymer mandrel of the appropriate diameter. The inner layer 62 is thenover-braided with a synthetic fiber braid layer 64 of approximately0.002 to 0.003 inches in diameter. In a preferred embodiment thesynthetic fiber is Pen monofilament from Biogeneral Advanced FiberTechnology. Next a second coat of elastomeric material is extruded overthe braided inner layer to create the outer layer 66. The inner layer 62and the outer layer 66 may be made from elastomers having the same shorehardness or from materials having different shore hardnesses.Preferably, the elastomer is PEBAX or Pellethane due to processabilityand high heat deflection temperatures.

After the outer layer 66 of elastomeric material is applied, the outsideof the outer layer 66 is centerless ground to the desired finishedoutside diameter French size. The acetyl mandrel is removed and thecenter strut 80 is inserted through the center of the elastomeric tube60. A half-moon elongated spacer made from a high temperature polymersuch as PEEK, Teflon or liquid crystal polymer may be inserted into bothsides of the inner diameter of the elastomeric tube 60 to stabilize andcenter the center strut 80 with respect to the center of thelongitudinal axis of the elastomeric tube. This interim assembly isplaced in the device depicted in FIG. 12.

Clamps 103 a and 103 b are used to clamp both longitudinal ends of thecenter strut 80. The clamps 103 a and 103 b of the device of FIG. 12 areconstructed from an electrically conductive material such as copper.Clamp 103 b retracts and puts the strut under controlled tension using apneumatic push-pull cylinder 104 or alternate automatically controlledtensioning means. The interim assembly is then nested and constrained intwo fixtures 102 a and 102 b having half-cylindrical indentationsadapted to receive the assembly. Fixtures 102 a and 102 b when matedtogether by using fixture adjustment mechanism 106 a and 106 b placepressure on the interim assembly in order to limit localized heatdistortion in the outside tip diameter. Fixtures 102 a and 102 b may beconstructed from high heat transfer materials such as aluminum orcopper. A proportional-integral-derivative (PID) temperature feedbackloop controls electrical current introduced between the clamps 103 a and103 b in order to heat the center strut 80 thereby causing the innerlayer 62 inner diameter to thermally bond with both thin longitudinalsides of the center strut 80 to define a composite structure withinseparable members. The strut temperature is monitored using atemperature feedback sensor 105, preferably a non-contact, fast responsetime thermopile based infrared sensor that senses the strut surfacetemperature.

One method for heating the center strut using the device shown in FIG.12 uses the feedback controlled power circuit depicted in FIG. 13D. Aninfrared temperature sensor 510 monitors the temperature of the heatedcenter strut 80 and provides an input voltage to a programmable logiccontroller (PLC) 520 analog to digital converter module. The PLC 520controls the analog switching solid state relay 530 with a built insynchronization circuit to control low-voltage, (5-28 VAC) 50-60 hertzalternating current by varying the phase-angle to rapidly heat thecenter strut 80. The proportional, integral, and derivative (PID) looptemperature feedback control by the PLC enables the strut temperature tobe monitored and the PLC adjusts the phase angle accordingly to achievethe correct temperature set point. The line voltage, AC load current andcontrol input to the analog switching solid state relay 530 can be seenin FIGS. 13A-C respectively. The circuit is powered by 120V AC linevoltage 501 controlled by switch 502 and protected by 10 amp fuse 503which is stepped down using transformer 505 resulting in 12-24 V ACoutput.

An alternate method for closed loop heating of the center strut is shownin FIGS. 14A-D. In the schematic of FIG. 14D for the heating powercontrol circuitry, line voltage (120V AC) 601 controlled by switch 602and protected by 10 amp fuse 603 is stepped down and converted into12-24 V DC using step down transformer 604 and bridge rectifier 605. Adirect current solid state relay 630 is used to rapidly switch (on-off)5-24 volt direct current using a time proportioning control PID loopalgorithm that controls the mosfet or transistor output of theprogrammable logic controller 620 to the solid state relay control side.The control output pulse width and duration is dependent on the analogtemperature measurement feedback from the thermopile based infraredsensor 610 to the PLC.

Once heating is completed, the tension is removed from the from thestrut by translating clamp 103 a using the pneumatic push pull cylinderand the two halves of fixture 102 a and 102 b are retracted away fromthe assembly using fixture adjustment mechanisms 106 a and 106 b.

The distal tip section 34 with bonded center strut can then be affixedto the proximal section 32 as discussed above. The tip electrode 34 isaffixed to the distal end of the distal tip section 34 and one of thelead wires 70 is attached to the electrode. A puller wire 44 or pullerwires 44 a and 44 b are attached to the distal end using one of thearrangements discussed above. If the tip electrode contains fluid ports39 then an irrigation lumen 90 is attached to the tip electrode and isrouted through one of the two lumens.

One additional step in the manufacturing process is the roughening ofside edges of the center strut 80 to create abrasions of approximately250-500 micro inches to improve adhesion to the inner diameter of theelastomeric tube

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention.

Accordingly, the foregoing description should not be read as pertainingonly to the precise structures described and illustrated in theaccompanying drawings, but rather should be read consistent with and assupport to the following claims which are to have their fullest and fairscope.

What is claimed is:
 1. A catheter for use in a vessel comprising: anelongate tubular member having a proximal end and a distal end andhaving a first lumen disposed therein; a tip electrode disposed at thedistal end of the tubular member; a center strut extending from near theproximal end of the tip electrode through a deflectable distal portionof the elongate tubular member and having a first longitudinal edge anda second longitudinal edge; wherein the center strut is bonded to theelongate tubular member along substantially the entire length of thefirst longitudinal edge and the second longitudinal edge to create aninseparable composite structure from the center strut and the elongatetubular member having a cross-sectional moment of inertia that remainssubstantially constant along the entire length of the compositestructure.
 2. The catheter of claim 1 wherein the center strut has beenthermally bonded to the elongate tubular member along substantially theentire length of the first longitudinal edge and the second longitudinaledge.
 3. The catheter of claim 1 further comprising a pull wire, havinga proximal end and a distal end, for causing the deflectable distalportion of the elongate tubular member to deflect wherein the proximalend of the pull wire is attached to a control handle at the distal endof the catheter.
 4. The catheter of claim 3 wherein the distal end ofthe pull wire is attached to the tip electrode.
 5. The catheter of claim1 further comprising a first pull wire and a second pull wire, eachhaving a proximal end and a distal end, wherein the proximal end of thefirst and second pull wires are attached to a control handle and thedistal end of the first pull wire is attached to a first face of thecenter strut and the distal end of the second pull wire is attached tothe second face of the center strut.
 6. The catheter of claim 5 whereinthe center strut comprises at least one anchor hole for attachment ofthe distal ends of the first and second pull wires.
 7. The catheter ofclaim 5 wherein the center strut comprises a plurality of anchor holeslongitudinally spaced along the length of the center strut forattachment of the distal end of the first and second pull wires.
 8. Thecatheter of claim 7 wherein the plurality of anchor holes are spacedfrom adjacent anchor holes by approximately 0.078 inch.
 9. The catheterof claim 7 wherein the anchor holes are approximately 0.015 inch indiameter.
 10. The catheter of claim 1 further comprising a first pullwire and a second pull wire each having a proximal end and a distal end,wherein the proximal ends of the first and second pull wires areattached to a control handle and the distal ends of the first and secondpull wires are attached to the tip electrode.
 11. The catheter of claim10 wherein the tip electrode is comprised of a hollow portion and a plugand the distal ends of the first and second pull wires are attached tothe plug prior to insertion in the hollow portion.
 12. The catheter ofclaim 1 further comprising a temperature sensor.
 13. The catheter ofclaim 1 further comprising a location sensor.
 14. The catheter of claim1 wherein the tip electrode has at least one irrigation port and thecatheter further comprises an irrigation lumen in communication with theirrigation port.
 15. The catheter of claim 14 wherein the tip electrodecomprises a plurality of irrigation ports.
 16. The catheter of claim 1further comprising a first pull wire and a second pull wire each havinga proximal end and a distal end, wherein the proximal ends of the firstand second pull wires are attached to a control handle and the distalends of the first and second pull wires are attached to anchors and arethreaded through first and second holes in the tubular member.
 17. Thecatheter of claim 1 wherein the tubular member has an inner layer, abraided layer and an outer layer along its entire length and wherein thefirst longitudinal edge and the second longitudinal edge of the centerstrut is thermally bonded to the inner layer of the tubular member alongthe entire length of the first longitudinal edge and the secondlongitudinal edge of the strut.
 18. The catheter of claim 1 wherein thefirst and second longitudinal edges of the center strut compriseroughened areas to improve bonding with the tubular member.
 19. Thecatheter of claim 1 further comprising a molded coupling adapted toreceive the proximal end portion of the tip electrode.
 20. The catheterof claim 19 wherein the distal end of the center strut comprises atleast one snap-fit notch and the molded coupling further comprises atleast one snap-fit wedge adapted to receive the snap-fit notch.
 21. Thecatheter of claim 20 wherein the snap-fit notch and snap-fit wedge locktogether in a one-way manner in order to secure the center strut in themolded coupling.
 22. The catheter of claim 19 wherein the moldedcoupling further comprises at least one slot adapted to receive at leastone of the first or second longitudinal edges of the distal portion ofthe center strut.
 23. A catheter for use in a vessel comprising: anelongate tubular member having a proximal end and a distal end andhaving a first lumen disposed therein; a tip electrode disposed at thedistal end of the tubular member; a center strut extending from near theproximal end of the tip electrode through a deflectable distal portionof the elongate tubular member and having a first longitudinal edge anda second longitudinal edge; a molded coupling having a distal portionadapted to receive a portion of the proximal end of the tip electrodeand having a proximal portion having at least one slot adapted toreceive at least one of the first or second longitudinal edges of thecenter strut; wherein the center strut is bonded to the elongate tubularmember substantially along entire length of the first longitudinal edgeand the second longitudinal edge to create an inseparable compositestructure of the center strut and the elongate tubular member having across-sectional moment of inertia that remains substantially constantalong the entire length of the composite structure.
 24. The catheter ofclaim 23 wherein the distal end of the center strut comprises at leastone snap-fit notch and the molded coupling further comprises at leastone snap-fit wedge adapted to receive the snap-fit notch.